The use of resin-coated proppants or propping agents is increasingly important in treating subterranean formations. In hydraulic fracturing, particles such as sand are coated and used to maintain a fracture formation in a propped open condition. The coating improves the stability of proppants at high closure stresses. Sand or similar substrates have been coated with resins such as an epoxy, furan, or phenolic resin to create proppants. Fracturing of the subterranean formation is conducted to increase oil and/or gas production. Fracturing is caused by injecting a viscous fracturing fluid or a foam at a high pressure into the well to form the fracture. Proppants are used to increase production of oil and/or gas by providing a conductive channel in the formation. As the fracture is formed, the proppant is placed in the formation to maintain the fracture in a propped condition when the injection pressure is released. As the fracture forms, the proppants are carried into the fracture by suspending them in additional fluid or foam to fill the fracture with a slurry of proppant in the fluid or foam. Upon release of the pressure, the proppants form a pack that serves to hold open the fractures. The propped fracture thus provides a highly conductive channel in the formation.
Coating particles, such as sand and the like, with resins is relatively complex when heating the particle or sand is required to melt the resin. It is necessary to heat only the surface of the sand grain and not the interior of the grain. This is an expensive process which requires a considerable amount of time, monitoring, precise control and production of heat. Control systems can be designed to reliably control physical system components in the presence of external disturbances, variations among physical components due to manufacturing tolerances, and changes in inputted set-point values for controlled output values. Control systems usually have at least one measuring device, which provides a reading of a process variable, which can be fed to a computer controller, which then can provide a control signal to an actuator, which then drives a final control element acting on, for example, a flow stream of heat or product. Examples of final control elements include flow control valves, speed controlled pumps, conveyors, augers, and screws. A control system, in some cases, can be designed to remain stable and avoid oscillations within a range of specific operating conditions. A well-designed control system can, in some cases, significantly reduce the need for human intervention, even during upset conditions in an operating process, and reduce the time and cost of manufacturing a product.
Control systems for heating sand, mixing and coating heated sand, and final coated sand flow processing are not completely continuous. A completely continuous process for making a final product of coated sand would significantly improve the quality of the final product while reducing its cost.